Unburned fuel and other combustion products may escape past the piston of an internal combustion engine (e.g., an internal combustion engine of a vehicle) into the crankcase. The resulting gases in the crankcase, often referred to as “blow-by” gases, may contribute to the formation of sludge in the engine oil supply. Further, blow-by gases may excessively pressurize the crankcase, resulting in undesirable leakage of oil pan gasket and crankcase seals. To avoid these issues, an engine may include a crankcase ventilation (CV) system coupled to the intake, which serves to vent blow-by gases from the crankcase to the intake. The CV system may include a passive crankcase ventilation (CV) valve intermediate the crankcase and the engine intake passage, to regulate the flow of blow-by gases from the crankcase to the intake manifold.
One example approach to purging a crankcase in a turbocharged engine is shown by Ulrey et al. in U.S. 2014/0116399. Therein, vapors from the crankcase are drawn into a suction port of an aspirator as the aspirator generates vacuum via compressor bypass flow during boosted conditions. During conditions when the engine is not boosted, vapors from the crankcase are directed to the intake manifold.
The inventors herein have recognized a potential issue with the example approach in U.S. 2014/0116399. As an example, the crankcase may still be over-pressurized (e.g., with a higher amount of positive pressure) during boosted conditions when the aspirator is clogged. For example, crankcase vapors that flow through the aspirator may cause a higher level of humidity in the aspirator. During cooler ambient conditions, the aspirator may be susceptible to frost formation and resulting aspirator blockage at a throat of the aspirator. Accordingly, vapors in the crankcase may not be evacuated during subsequent boosted conditions leading to a higher than desirable positive pressure in the crankcase. This increased pressure in the crankcase may degrade the crankcase seals causing leaks and eventual degradation of engine performance and durability.
The inventors herein have identified approaches to at least partially address the above issues. An example approach includes a method for a boosted engine comprising, during a first condition, generating vacuum at an aspirator positioned in a compressor bypass passage, using the vacuum to draw gases from a crankcase, and reducing a pressure in the crankcase, and during a second condition, reducing the pressure in the crankcase via a bypass passage coupled to an intake passage and crankcase. In this way, crankcase vapors may be evacuated via the bypass passage reducing a likelihood of crankcase pressurization.
As one example, a boosted engine may include a compressor with an aspirator arranged across the compressor in a compressor bypass passage. A suction port of the aspirator may be fluidically coupled with a crankcase of the boosted engine. The aspirator may generate vacuum during boosted engine operation via flow of compressed air in the compressor bypass passage, the compressed air flowing from an outlet of a compressor to an inlet of the compressor. Further, an aspirator bypass passage may fluidically couple the crankcase to the inlet of the compressor such that fluid flow through the aspirator bypass passage circumvents the aspirator. Thus, when the aspirator allows compressor bypass flow therethrough (e.g., with aspirator not plugged), vacuum generated at the aspirator draws crankcase vapors into the suction port of the aspirator. However, if the aspirator is blocked, crankcase vapors may then flow via the aspirator bypass passage into the inlet of the compressor.
In this way, crankcase over-pressurization may be reduced. Positive pressure in the crankcase during boosted conditions may be relieved by flowing crankcase vapors to the compressor inlet via the aspirator bypass passage if the aspirator is blocked. By reducing a likelihood of excessive pressure in the crankcase, degradation of oil seals in the crankcase may be reduced. Further still, leaks may be averted enabling an improvement in engine performance. Overall, durability of the boosted engine may be enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.